Current limiting relay



April\28, 1942. P. R. LEE 2,280,960y CURRENT LIMITING RELAY Filed Oct. 20, 1959 2 Sheets-Sheet l WM. BY

April 28, 1942.

P. R. LEE

CURRENT LIMITING RELAY Filed 001;. 20, 1939 2 Sheets-Sheet 2 TTORNEY My invention relates to the thermal Patented Apr. 28, 1942 n UNITED STATES PATENT OFFICE l :.gsosso consum' mums. amr

sylvania Ohio, assignor to West- Company,

a corporation oi' Penn- Application October 20, 1939, Serial No. 300,421

(Cl. 20o-113) 3 Claims.

relays and more particularly to a. temperature-compensated adjustable relay.

With the increasing use of both electric ranges and water heaters there is, in a large number of territories, a tendency for localized load-peaks to occur on distribution systems. These peaks usually occur on residential lines in the early evening hours, or at times when there is the possibility of both the household range and water heater being energized. To eliminate the possibility of distribution failures from such localized peaks the power companies have been required to install larger equipment, which requires substantially increased expenditures without any commensurate increase in return for such companies. To overcome this substantial increase in expenditure, I propose that the power companies install an inexpensive relay which will limit the power usage at each house which has both an electric range and water heater. In other Words, the localized'load-peaks would be eliminated at their source.

It is therefore an object of my invention to provide an inexpensive, rugged, eincient relay which may be installed in series with the supply circuit of each of those homes which have both an electric range and water heater and asso-v ciated with the water heater so as to disconnect such Water heater from the supply circuit when the maximum permissible normal load of the house has been reached.

A further object of my invention is to provide a thermal relay connected in a selected circuit and which, when the current ilowing in the circuit exceeds a predetermined amount, will operate to reduce the ilow of current within the circuit.

A further object of my invention is to provide a thermal relay adapted to limit the ilow of current passing through a circuit, with means associated therewith 'for compensating for the changes in ambient temperature.

Another object of my invention is to provide a thermal relay having means for compensating for the changes in the ambient temperature surrounding such relay, with adjustable means associated therewith for selectively adjusting the operations of such device.

Other objects of my invention will either be pointed out specically in the course of the following description of a device embodying my invention, or will be apparent from such description.

In the accompanying drawings:

Figures 1 and 2 are top and side elevational views, respectively, of a thermal relay embodying my'inventicn;

Fig. 3 is a sectional view, taken along the line III-III of Fig. 1 with the relay in its inoperative position;

Fig. 4 is an end view taken from the left-hand end of Fia-2;

Fig. 5 is a sectional view taken along the line trating the method of connecting the relay to a the secondary or controlled house load.

Referring to the accompanying drawings, in which like reference characters indicate like parts in the several iigures, I show a thermal relay I0 comprising a supporting structure I 2, a main bimetallic or thermal responsive element I4 adapted to carry current, a secondary bimetallic or thermostatic element i6 adapted to compensate for changes in the ambient temperature, main cooperating contacts I8 controlled by the respective bimetallic elements I4 and I6, and secondary contacts 20 adapted to shunt or limit the amount of current passing through the main element I4 under conditions of abnormally large power usage.

The supporting structure I2 comprises, in this instance, two plate-like members 2Ic and 2Ib rigidly attached together by means of suitable pin or rivet structures 22. Plate 2Ia is positioned on top of the structure, while plate 2lb is located on the bottom. The pin structures 22 are adapted to space the plates apart from each other to enable the operating mechanism of the relay to be located therebetween and rigidly attached thereto.

Auxiliary or secondary terminal straps 24 are rigidly attached to the supporting structure I2 at one end thereof. One terminal strap 24 is insulatedlyattached to the upper plate 2 Ia, while the second terminal strap 24 is insulatedly attached to the lower plate 2lb. The terminal straps 24 are adapted to have attached thereto circuit, and are exibly associated with the main cooperating contacts I8 as hereinafter described. Main termin nals or terminal straps 26, being two in number, are insulatedly and rigidly attached to the lower plate 2lb, by means of suitable rivetstructures 28. The straps 26 are, in this instance, elongated relatively narrow members which extend along lthe lower plate 2Ib. The outer or terminal ends of such straps are offset upwardly so as to be in line with the main bimetallic member I4. The inner ends of such straps 26 support the stationary contact 60 of the secondary contacts 20 below the bimetallic member I4.

The main bimetallic element or thermal responsive member I4 comprises, in this instance a U-shaped member (see Fig. 7). Such bimetallic member is rigidly attached to the supporting structure I2 by means of the rivets 28 and is rigidly and electrically attached to the terminal straps 26 by means of suitable rivets 30. However, such bimetal may be welded to the terminals 26 in place of the rivets 38, if desired. The open or tine ends of the bimetallic element are, in this instance, rigidly attached to the straps 26 whereas the closed or main end of the bimetallic element' I4 is positioned within the relay I8. Each tine of the element I4 is electrically associated with a separate terminal strap 26, and, therefore, it follows that, with the terminal straps 26 electrically connected in series orrparallel with the main or controllingcircuit, the current passing through the controlling circuit,or a current proportional thereto, will flow through the main bimetallic element I4. The bimetallic member is thus adapted to flex in response to the flow of current through such controlling circuit. In addition, the bimetallic member I4 inherently ilexes in response to changes in the ambient temperature, the amount of such ilexure being substantially the same in magnitude and direction as in the case of the compensating member I6.

Suitable means are located upon or rigidly attached to the free or inner end of the element I4 by an insulating strip 38 for rigidly and inlsulatedly attaching a movable contact 46 thereto, constituting one of the cooperating contacts i8 and being adapted to cooperate with the movable" contact 44 as hereinafter described. In addition, a shunting contact structure 32 is loosely attached to the free end of the bimetallic member and is electrically associated therewith. The shunting structure 32 is adapted to contact the inner ends of the terminal straps 26 and to connect such straps in shunt to the bimetallic member I4 as hereinafter described. It is to be understood that the shunting contact structure 32 need not be directly electrically associated with the bimetallic member I4 to connect the straps 26 in shunt thereto.

The secondary thermal responsive element I6 comprises, in this instance, a substantially U- siiaped member having relatively short tines. The secondary element I6 is resiliently attached to the supporting structure I8 by means of a liat spring or resilient member 34.4 The resilient member is rigidly attached to the tine end of the secondary element I6 at one end thereof and to suitable supporting posts 36, mounted on upper supporting plate member Zia, at the other end thereof. The bimetallic member I6 is thus adapted to resiliently flex about the supporting posts 36 in an obvious manner in response to ambient temperature. The amount of such ilexure is substantially the same, in magnitude and direction as the main bimetallic member I4.

The second or stationary contact 44 of the cooperating contacts I8 is insulatedly attached to 'the free end of the second bimetallic element I6 by means of a suitable insulating member or strip 38. Contact 44 is adapted to cooperate with the first contact 46 insulatedly attached to the free end of the main bimetallic element I4.

A suitable manually operable adjusting screw 40 is threadedly attached to upper plate 2Ia o f the supporting structure I by means of a bushing 42. The adjusting screw is positioned above and is adapted to contact the second bimetallic member I6 at a point relatively near its flexible mounting. The adjusting screw 48, acting in opposition to the natural bias of bimetallic element I6, is thus adaptedI to adjust the second thermal responsive element I6 either downwardly or upwardly to any desired position. This feature permits the thermostat to be readily adber I4 by means of an insulating member lIusted to any desired operating value. By running'they screw 48 down, the thermostat isA adjusted to effect disengagement of the cooperating contacts I8 with an increasingly higher current flowing through the main bimetallic element I4.r Conversely, with the screw being run up within the bushing 42 the contacts will become disengaged with a decreasingly lower flow of current through the controlling circuit.

The cooperating contacts I8 comprise, in this instance, the contact members 44 and 46 which are rigidly attached to'the second bimetallic member I6 andto the main bimetallic mem- 88 and insulating member 39, respectively. In addition to being rigidly attached to, and insulated from, the free ends of the bimetallic members I4 and I6, the contacts 44 and 45 are flexibly and electrically attached to the secondary terminal straps 24 by means of suitable flexible leads 48 and 50. The flexible leads 48 and 5I) are rigidly attached to the movable contacts 44 and y46 by means of suitable strap-like members 52 and 54, respectively (see Fig. 5). The straplike members are, in this instance, adapted to llt about the insulating members 38 and 89 and have suitable overhanging flanges outwardly displaced from the insulating members for permitn ting the flexible leads 48 and 50 to be'squeezably attached thereto.

The flexible leads 48 and 50, while being connected to the movable contacts 44 and 46respectively, which, in turn, are movable with the bimetallic members I4 and I6 do not materially restrict the movements of such bimetallic members. The flexible leads 48 and 50 are rigidly attached to, and electrically associated with, the terminals 24 by means of lsuitable insulating members and rivet structures 56 in a well known manner. It is therefore obvious that current may readily pass through the terminal straps 24, flexible leads 48 and 50, and cooperating contacts 44 and 46 when closed.

The secondary or shunting contacts 28 include a suitable movable contact 58 preferably loosely attached to the lower surface of the main bi-v metal I4 and a stationary contact 68 located upon the inner free end of each of the main terminal straps 26. The cooperating contacts 28 are adapted to become engaged and limit the downward flexing action of the main bimetallic member I4 when an abnormally heavy load or current is flowing through that member. The cooperation of such contacts 58 Vand 60 serves to connect the terminal straps 26 in parallel with or in shunt to bimetallic member I4 and materially reduce the flow of current therethrough as hereinafter described.

The relay II) ls electrically associated with a variablenormal house load, such as a range, re-

frigerator, lights, etc., and a heavy load appliance, such as a water heater or the like, in substantially the following manner. One side of the variable normal load is connected to the power supply 62 by line 64. The other side of such load is then connected to the power supply by line 66, bimetallic member I4 and line 68. The shunting terminals 26 are also connected to the line 68 at one end and are adapted to be connected in parallel with the member I4 upon the engagement of contacts 58 and 60 to reduce the flow of current through the bimetal upon an abnormallylarge normal load. The heavy load appliance is connected to the power supply 62 in parallel with the variable normal load byk means of line and III, and line 'I2 cooperating contacts I8, line 'I4 and 68. The passage of current through the heavy load appliance accordingly,

of current passing through the variable normal load and main bimetallic member I4. l

The bimetallic elements I4 and I6 are mounted with respect to each other so thatthey will move in a complementary manner with changes in the ambient temperature. That is, the two bimetallic members I4 and I6 will each flex substantially the same magnitude and direction with all changes in the ambient temperature. In other words, the two bimetallic members have similar thermal characteristics whereby they flex a. similar amount in response to changes of temperature which affect both similarly. This charactei'istic ensures that the relay will operate yat its predetermined set value regardless of the ambient temperature or the changes in such ambient temperature.

When operating the thermal relay embodying my invention, in association with, say, a dwelling house load, in which there is a plurality of heavy current-consuming apparatus, one of which it may be desired to deenergize during periods of abnormal load conditions, the main bimetallic member I4 is connected in series with the supply circuit (see Fig. 8). However, it is preferred that the main bimetallic member I4 be connected in series with the supply circuit exclusive of the heavy apparatus as hereinabove described to prevent the main contacts I8 of such relay from hunting or flickering.

The cooperating contacts I8 are connected in series with one of the heavy load appliances, such as a water heater, which it is desired to deenergize during such abnormal load conditions. Assuming the controlling circuit is drawing a normal amount of power, under the maximum permissible value, the main bimetallic element vI4 will remain in its upper or engaged position (see Fig. 2). However, with a continued increase of the load of the controlling or main house circuit the main bimetallic element I4 will increase in temperature due to the flow of such current therethrough. Should such current increase above a predetermined maximum value, the bimetallic element would correspondingly increase in temperature and flex downwardly so as to disengage the cooperating contacts I8.

Upon the disengagement'of the cooperating contacts I8 the heavy load appliance or water heater operatively associated therewith would be disconnected from the power supply. In this way, the load consumed by the dwelling house is suitably reduced. However, the bimetallic element; I4 being connected to the normal load and not directly with the water heater, such element will remain in the contact-open position during a suitable period ofv time, or until the current flowing through the main bimetallic element is reduced belowV the predetermined maximum value. The contacts I8 then become reengaged, permitting the heavy load appliance to be reconnected to the supply circuits.

However, should the vnormal house load, such as lights and the range, draw a current above the predetermined maximum value, the bimetallic element I4 would again move or flex downwardly. This action would normally occur only during the evening hours, or at such other time as the housewife would be normally using the electric range.

With the range connected to the power supply, the flow of current through the main bimetallic member I4 may be substantially' above said maximum value whereupon such element will continue 'to flex downwardly. The downward exing action or movement of the bimetallic element I4 under such abnormal conditions will be limited by means of cooperation of the-secondary contacts 20. As the secondary contacts 20 become engaged, the terminal straps 26 are connected in parallel with the bimetallic element I4, as traced above, thereby limiting its downward travel. This cooperative action correspondingly reduces the flow of current through the bimetallic element I4 and permits the bimetallic member to cool and thereby avoid excessive bimetal temperature. In addition, such member may thus start to return to its normal position upon such reduction of the normal load. This action may result in a so-called hunting action of contacts 20. However, the voltage across such contacts is exceptionally small as a result of which there will be very little, if any, arcing therebetween as such contacts become disengaged. However, this action does not affect the normal flow of incoming current to the household.

Upon the reduction of power or ilow of current in the main household circuit to its normal operating value, the bimetal I4 will then return to its normal substantially horizontal position, permitting the contacts I8 to reengage. The heavy load appliance such as a water heater will thereby be reconnected to the power supply.

It is therefore obvious that the thermal relay embodying my invention, when connected in series with the load of a normal home, will tend to limit the flow of current of such home. In other words, the relay will tend to eliminate any localized peak-load conditions which might otherwise occur throughout the residential districts during the early evening hours.

It is to be understood that while this relay is described as being associated with a dwelling house for the -purpose of reducing the flow of current thereto, such structure may be used in any other desired manner or may be associated with any other-suitable circuit.

Various modifications may be made in the device embodying my invention without departing from the spirit and scope thereof, and I desire, therefore, that only such limitations shall be placed thereon as are imposed by the prior art and the appended claims.

I claim as my invention:

1. In a current limiting device for a dwelling house electric power circuit which disconnects a portion of the household circuit when the total power demand of the household is above a predetermined value, the combination of a supporting structure, a rst bimetallic member resiliently attached to the supporting structure, a movable contact insulatedly attached to said bimetallic member, a terminal means insulatedly attached to the supporting structure, means connecting the movable contact and the terminal means comprising at' least in part a flexible strap, a second bimetallic member attached to the supporting structure, said members moving in a common directiona like amount with changes in ambient temperature, a second movable contact insulatedly attached to the second bimetallic member, said second contact engaging said first contact during normal operations of the device,

a second terminal means attached to the supporting structure, means at least in part flexible connecting the second contact with the second terminal means, two main terminal means positioned upon and insulated from the supporting structure, contact means positioned upon the upper surfaces oi the inner ends of the main terminal means, said second bimetallic member being attached to the main terminal means whereby said second bimetallic member is in series with such main terminals, a jumper contact attached to the second bimetallic member so as to engage the contact means upon the terminal means when said second bimetallic member has exed to its fully open position whereby the current normally flowing through the second bimetallic member will be shunted through saidlmain terminal means, said second bimetallic member flexing in response to vthe passage of a current through the main terminals whereby upon such current increasing above a predetermined value said member will flex so as to disengage the cooperating flrst and second contacts, and adjusting means supported by the supporting structure and engaging the ilrst bimetallic member for ad- Justably positioning such member to selectively determine the predetermined current for disengaging said first and second contacts.

2. In a current limiting device for a dwelling house electric power circuit which disconnects a portion of the household circuit when the total power demand of the household is above a predetermined value, the combination of a supporting structure, a rst bimetallic member resiliently attached to the supporting structure substantially parallel thereto, a movable contact insulatedly attached to said bimetallic member, a terminal means insulatedly attached to the supporting structure, means connecting the movable contact and the terminal means comprising at least in part of flexible strap, a second bimetallic member attached to the supporting structure substantially parallel thereto, said second bimetallic member being positioned beneath and substantially parallel to the first bimetallic member, said members moving in a common direction alike amount with changes in ambient temperature, a second movable contact lnsulatedly attached to the second bimetallic member, said second contact being positioned below the first contact and engaging said first contact during normal operations of the device, a second terminal means attached to the supporting structure, means at least in part flexible connecting the second contact with the second terminal means, two main terminal means having at least a part thereof positioned upon and insulated from the supporting structure intermediate the second bimetallic member and said structure, contact means positioned upon the upper surfaces of the inner ends of the main terminal means, said second bimetallic member having two outwardly extending portions joined at their inner ends to form a U- shaped member, the outer ends of said portions being attached to the main terminal means whereby said second bimetallic member is ln series with such main terminals, a jumper contact attached to the second bimetallic member so as to engage the contact means upon the terminal means when said second bimetallic member has iiexed to its fully open position whereby the current normally flowing through the second bimetallic member will be shunted through said main terminal means. said second bimetallic member flexing in response to the passage of va. current through the main terminals whereby upon such current increasing above a predetermined value said member will ilex so as to disengage the cooperating first and second contacts,

and adjusting means supported by the supporting structure and engaging the first bimetallic member for adlustably 'positioning such `member to selectively determine the predetermined'current for disengaging said rst and second contacts.

3. In a current limitlng'device for a dwelling house electric power circuit which .disconnects a portion of the household circuit when the total power demand of the household is above a predetermined value, the combination of a supporting structure having parallel portions one above the other, a ilrst bimetallic member resiliently attached to the upper portion of the supporting substantially parallel thereto and elevated therefrom, said second bimetallic member being positioned beneath and substantially parallel to the first bimetallic member, said members moving in a common direction a like amount with changes in ambient temperature, a second movable contact lnsulatedly attached to the second bimetallic member, said second contact being positioned below the first contact and engaging said first contact during normal operations of the device, a second terminal means attached to the lower supporting structure, means at least in part ilexible connecting the second contact with the second terminal means, two main terminal means having at least a part thereof positioned upon and insulated from the lower portion oi the supporting stucture intermediate the second bil metallic member and said structure, contact means positioned upon the upper surfaces of the inner ends of the main terminal means, said second bimetallic member having two outwardly extending portions joined at their inner ends to form a U-shaped member, the outer ends of said portions being attached to the main terminal means whereby said second bimetallic member is in series with such main terminals, a jumper contact attached to the second bimetallic member so as to engage the contact means upon the terminal means when said second bimetallic member has iiexed to its fully open position whereby the current normally owing through the second bimetallic member will be shunted through said main terminal means, said second bimetallic member ilexingdownwardly in response to the passage of a current through the main terminals whereby upon such current increasing above a predetermined value said member will flex downwardly so as to disengage the cooperating first and second contacts, and adjusting means supported by the upper portion of the supporting structure and engaging the iirst bimetallic member for adjustably positioning such member to selectively determine the predetermined current for disengaglng said first and second contacts. v

PAUL R. LEE. 

